Doctors for paper and like machines



June 16, 1959 H. E. B. scoTT 2,890,473

nocroas FOR PAPER AND LIKE MACHINES Filed Dec. 14. 1954 2 Sheets-Sheet 1H. E. B. SCOTT DOCTORS FOR PAPER AND LIKE MACHINES June 16, 1959 2Sheets-Sheet 2 Filed Dec. 14, 1954 e m W United States atent DOCTORS FORPAPER AND LIKE MACHINES Harold Eric 'Baiiol Scott, Weybridge, England,assignor to Vickerys Limited, London, England Application December 14,1954, Serial No. 475,083

9 Claims. (Cl. 15-2565) This invention relates to doctors for papermaking and other machines, including rolls or cylinders which have to bekept clean, e.g. board making machines, pulp making machines, milkdriers, metal foil rolling mills and gluing, crimping or combiningmachines.

More specifically, the invention relates to that type of doctor whichcomprises a holder, a doctor blade having its rear edge retained in theholder and a pressure plate, disposed above the blade and bearingagainst the upper surface of the blade throughout the whole, orsubstantially the whole, of the length of the blade.

A doctor in a paper making machine normally serves merely to clean theroll to which it is fitted by removing pulp and other impuritiesdeposited on the roll by the web of paper. From time totime, however,the web of paper breaks and the doctor then performs the furtherfunction of stripping the web from the roll and preventing the web fromwinding itself around the roll.

The holder is normally extruded from brass or manganese bronze with alip to retain the rear edge of the blade. Due to the fact that theholder is extruded, the upper lip of said retaining groove must be ofsubstantial depth, with the result that the pressure plate is inclinedat a substantial angle to the blade. This renders more difficult therearward escape of the pulp.

Moreover, the rear edge of the pressure plate is normally alsoaccommodated in a groove in the holder with a nose at the top of theholder bearing against the upper surface of the pressure plate near itsrear end and it has hitherto been necessary to make this nose ofsubstantial depth. This tendency has been accentuated by the fact thatit is the usual practice to retain the pressure plate in the holder byrivets projecting from its undersurface and engaging in a longitudinalgroove in the holder, the heads of the rivets projecting above the uppersurface of the pressure plate, and thereby necessitating a clearancebetween said upper surface and the top of the retaining groove. The noseof the holder therefore necessarily slants upwardly and rearwardly fromthe upper surface of the pressure plate at a fairly steep angle of 30degrees or more. Consequently, pulp scraped from the roll and travellingrearwardly along the upper surfaces of the blade and pressure plate ischecked by the ramp formed by the sloping surface of the nose andaccumulates in front of the ramp necessitating frequent cleaning of thedoctor.

The present invention provides a doctor of the above type of streamlinedform and such that the pulp or web of paper can travel freely along theupper surface of the pressure plate along and over the holder. Thesmooth streamlined shape of the upper surface of the whole constructionis of particular importance on modern fast and wide paper makingmachines, which run often at 2, Q0 feet per minute or over and where theslightest obstruction to the web, should the paper break, would cause abunch-up. At this high speed the broken paper is liable to accumulate onthe doctor at such a fast rate 2,890,473 Patented June 16 1959 2 as tocause a bunch-up thus making the feeding up of the broken web verydifi'icult and causing added loss of paper. This tendency is reducedwith the doctor according to the invention. i

According to the invention, the rear or trailing edge of the blade,instead of being retained in a groove in the holder which .is open atthe front or leading side only, is accommodated in an open-topped slotin the holder and is retained in said slot by a keep plate, the uppersurface of which is in contact with the undersurface of the pressureplate. This keep plate can be considerably thinner than theabove-mentioned extruded lip and consequently the angle between thepressure plate and the blade may be considerably reduced, e.g. to theorder of 5 degrees-or less. This has the advantage of facilitating therearward travel of the pulp on the upper surface of the blade. to thepressure plate and the blade being nearly parallel, the pressure platecan be of thicker material to resist the impact of the web at high speedand at the same time allow flexibility of movement of the blade. Also,the flexibility of the unsupported portion of the blade is increased.Moreover, since a groove closed at the top is no longer required in theholder, the-latter canbe made by machining from the solid bar stock,which enables the holder to be made of harder or stronger material, e.g.high tensile or stainless steel, which cannot be extruded.

Preferably the blade-retaining slot in the holder comprises a seatingfor the rear edge of the blade, and a portion accommodating lugsprojecting from the blade near its rear edge. The keep plate isconveniently retained in position by lugsextending. downwardly from thepressure plate, through holes in the keep plate, into :1 longitudinalslot in the holder.

The pressure plate may be :bevelled at its forward edge, to provide agradual rise from the upper surface of the blade, and abut with justsliding clearance at its rear end against the vundersurface of' a noseon the holder, the angle between the .upper surface of the nose and theupper surface of the pressure plate being 15 degrees or less. Due to thebevel of the front of the pressure plate, and the small angle of theramp afforded by the forward end of the nose, pulp or paper can travelwith minimum obstruction from the upper surface of the blade onto andover the nose. The pressure plate may be retained in the holder by lugswelded onto its undersurface or by punched out downwardly extendingprojections.

As an alternative, the pressure plate may extend rearwardly over theholder and be secured thereto near its rear edge. In this case the noseon the holder normally present above the pressure plate is eliminatedentirely, thus reducing still further the obstruction afforded rearwardtravel of the pulp.

Three embodiments of the doctor according to the invention will .now bedescribed in detail, by way of example, with reference to theaccompanying drawings, in which:

Fig. 1 is a side elevation, on a greatly reduced scale, showing thefirst form of doctor in position on the roll of a paper making machine;

Fig. 2 is a side elevation of this form of doctor on a larger scale;

Fig. 3 is an exploded view of the doctor shown in Fig. 2;

Fig. 4 is a diagram showing a typical known doctor installation fittedto a press roll of a paper making machine with broke conveyor;

Fig. 5 is a side elevation of'the second form of doctor according to theinvention, which is primarily intended for use in the installation.shown .in "Fig. 4;

Fig. .6 is acorresponding plan view, and

Fig. 7 is a side elevation of thethird form of doctor according to theinvention, which is also primarily intended for use in the installationshown in Fig. 4.

Like numerals designate like parts throughout the figures.

The doctor shown in Fig. 1 comprises a blade 10, supported in a metalholder 11, carried by a bracket 12 which is biased by a spring or bygravity so that the blade 10 bears on the surface of a roll 13.

Turning now to Figs. 2 and 3,.the holder 11 is made of separatelymachined upper and lower sections 14, 15 joined together by screws 16 orin 'my other suitable fashion. The upper section 14 hasa flatundersurface, to which the forward end of the nose 17 is inclined atabout 15 degrees. A pressure plate .18, extending the full length of theblade 10, bears against the upper surface of the blade, and a keep plate19, also extending the full length of the blade, retains the blade inthe holder. The rear part of the upper surface of the lower section 15is flat, the front portion being stepped down by the amount of thecombined thickness of the pressure plate 18 and keep plate 19. Thethickness of each of these plates is conveniently .030". The pressureplate 18 can be made of thicker material for heavier duties. At the rearof the stepped down portion is an open topped longitudinal slot 20 toaccommodate retaining projections 31 pressed out from the undersurfaceof the pressure plate near its rear edge, these projections passing withclearance through holes 22 in the keep plate. A further step down isprovided near the front of the lower section 15 of the holder toaccommodate the rear edge of the blade, and in front of this is an opentopped longitudinal slot 23 to accommodate retaining lugs 24 on theundersurface of the blade near its rear edge. At the rear of the portionof the slot 23 accommodating the lugs is a seating 123 for the rear edgeof the blade. The blade may be of metal .050 thick, or of syntheticplastic material Ma" thick. The upper surface of the pressure plate isbevelled at its front edge 25 and bears against the blade slightly inrear of its longitudinal center line. The pressure plate is inclined tothe blade at about Sdegrees. A bevel 26 is provided at the forward endof the nose 17 on the holder.

The forward edge of the blade 10 is bevelled at 27, but after a shortperiod of use the leading edge of the blade is worn away by contact withthe roll to form a heel 28.

The surfaces of the blade and pressure plate remote from the roll have,for convenience, been referred to as their upper surfaces. It will beappreciated that in cases where the doctor blade is mounted beneath theroll its upper surface will be located, in the space below its lowersurface.

Fig. 4 shows a doctor installation at present in common use on the pressrolls of paper making machines. The doctor 100 is shown applied to thepress roll 113, which operates on the pulp travelling forwards on thefelt 29. The doctor 100 is mounted on a downwardly inclined support 112and pulp removed from the press roll 113 travels over the doctor anddown the support onto a conveyor 30 running transversely to the felt.

Normally the doctor only serves to remove impurities from the press roll113 but sometimes the web of partially consolidated pulp on the feltbreaks and the doctor then has to strip this web from the roll 113.Existing doctors at present in use on high speed paper making machinesofier so much obstruction to rearward travel of the pulp over the bladeand its holder and onto the support 112 that, when the web breaks, thepulp tends to accumulate as indicated at 31 in Fig. 4,

r The forms of doctor shown in Figs. 6-7 are intended for use on pressrolls and are designed to offer minimum obstruction to rearward travelof the pulp over the doctor blade and its holder.

The doctor shown in Fig. and Fig. 6 is generally similar to that shownin Figs. 2 and 3, but the rear part 115 of the lower section 15 of theholder 11 is bent downwardly, as indicated, to facilitate thetravel ofthe pulp onto the support 112 (Fig. 4). The upper section of the holderis constituted by a number of thin, narrow, closely abutting scctions114, which may conveniently be 3 in width, each attached to the lowersection by a rivet 116. The upper section of the holder thus has anextremely shallow nose 117, formed with a bevel 26 at its forward end,and consequently offers very little obstruction to rearward travel ofthe pulp. Due to the fact that the rear part of the holder is bentdownwardly, the pulp is already travelling in a downward direction bythe time it encounters the heads of the rivets 116. It cannot thereforeaccumulate in front of the rivet heads even when the doctor is installedon a fast running machine. The top section of the holder is divided intoindividual closely abutting sections 114 because of the difliculty inbending a long sheet of material to form throughout its length a nose117 extending at the correct angle to the remainder of the sheet.

In the case of the doctor shown in Fig. 7. the pressure plate isextended rearwardly to constitute the top section of the holder 11. Thepressure plate is formed of individual narrow, closely abutting sections118, which may conveniently be 3" in width and which are united to thedownwardly bent rear portion 115 of the lower section of the holder bythe rivets 116. In this case therefore the holder has no nose situatedabove the pressure plate and obstruction to rearward travel of the pulpis reduced to a minimum.

I claim:

1. A doctor assembly adapted to engage a roll and comprising: a lowerelongated rigid holder member having a leading edge adjacent said rolland having formed therein two longitudinal grooves extending parallel tothe axis of the roll, the leading groove nearer the roll being at alower level than the trailing groove farther from the roll; an elongateddoctor blade having a forward portion extending beyond the leading edgeof the lower holder provided with an edge adapted to engage the roll anda rear portion having a trailing edge, said blade having spacedprojections adjacent its trailing edge, said blade extending rearwardlyto a point between said grooves. said projections being received in saidleading groove and said trailing edge being backed by a wall of thelower holder located between the grooves; a keep plate having leadingand trailing edges bearing on said lower holder member, the leading edgeof said keep plate overlying the trailing edge of said doctor blade tothe rear of said projections, the trailing edge of said keep plate overlying said trailing groove, being backed by a wall of said trailinggroove and having spaced perforations overlying the trailing groove; apressure plate in face contact with said keep plate, said pressure platehaving leading and trailing edges and being inclined at a low angle tosaid doctor blade with its leading edge contacting a medial widthwiseline on said doctor blade; projections formed on said pressure plate andentering the trailing groove through the perforations in said keepplate; an upper holder member having its leading edge beveled at a lowangle, said upper holder member bearing on the trailing side of saidlower holder member and overlying a portion only of the width of saidpressure plate, and means for fastening the upper holder member to thelower holder member for securing said blade, keep plate and pressureplate to said upper and lower holder members.

2. A doctor assembly as set forth in claim 1 in which the pressure platehas a beveled leading edge.

3. A doctor assembly as set forth in claim 1 in which the holder membersare bent downwardly at the rear of the pressure plate.

4. A doctor assembly as set forth in claim 1 in which the upper holdermember is made up of a plurality of thin, narrow, closely abuttingsections.

. A doctor assembly as set forth in claim 1 in which the pressure plateis inclined at an angle of not more than five degrees to the doctorblade.

6. A doctor assembly adapted to engage a roll comprising a rigidelongated holder member having one edge adjacent said roll and havingparallel longitudinal grooves near said edge; an elongated doctor bladeextending from a point beyond said edge to a point between said groovesand backed by a wall of the groove nearer said edge and havingprojections engaging said last mentioned groove; a keep plate overlyingthe other groove and the space between said grooves, said keep platehaving perforations overlying said other groove, a flexible elongatedpressure plate inclined at a low angle to the doctor blade and havingone edge bearing on a medial portion of said doctor blade, said pressureplate lying on said keep plate and having projections penetrating theperforations in the keep plate and engaging said other groove, and meansfor securing said pressure plate to said holder member.

7. A doctor assembly as set forth in claim 6 in which the pressure platehas a beveled leading edge.

8. A doctor assembly as set forth in claim 6 in which the holder memberis bent downwardly at the rear of the other groove.

9. A doctor assembly as set forth in claim 6 in which the pressure plateis made up of a plurality of narrow, closely abutting sections.

References Cited in the file of this patent UNITED STATES PATENTS1,803,925 Vedder et al. May 5, 1931 1,803,927 Vedder et al. May 5, 19312,287,350 Lodding June 23, 1942 2,300,908 Broughton Nov. 3, 19422,376,502 Overton May 22, 1945 2,418,706 Goyette Apr. 8, 1947 2,477,339Ljungquist July 26, 1949 2,673,494 Scott Mar. 30, 1954

